This proposal is for an image processing facility together with electron microscope attachments for low dose work. The facility will take maximum advantage of existing resources at the University of Pennsylvania in order to keep the required budget to a minimum. The major projects that will make use of the facility include the following studies: 1) Vertebrate skeletal myosin filament structure by image processing of images of transverse sections of the filaments for backbone structure, and negatively-stained, separated filaments of myosin crossbridge arrangement. 2) Structure of microtubules and flagella by computer processing of images obtained from frozen-hydrated specimens, using low dose electron microscopy. 3) Molecular structure of blood clotting proteins by coordinating electron microscopy image processing and X-ray crystallographic data obtained from protein crystals. 4) Membrane protein structure by computer image processing of electron micrographs of successively tilted specimens--to give three-dimensional reconstruction by Fourier analysis and synthesis, and correlation methods. 5) Myosin filament crossbridge arrangement in invertebrate muscle (negative staining of separated filament), and the three-dimensional structure of myosin crossbridges attached to actin in rigor skeletal muscle (from thin sections), using Fourier-based image processing of the electron micrographs. 6) Myosin crossbridge patterns from freeze-fractured, deep-etched and rotary-shadowed specimens, using Fourier-based image processing of electron micrographs.